That is absolute bunk. I work with people every day that are in their 50's, 60's and even 70's and raising children. A lot of them are grandparents, some are great-grandparents and some are foster parents. While it may be more challenging in some ways, most of these folks have more energy and commitment than the children's natural parents. In some cases it seems to keep them young and healthy. I myself was raised for the better part of 9 years by my great-grandmother and I wouldn't trade that part of my childhood for anything. Some of the older folks who are raising children are worth a dozen of their more youthul counterparts.